Mercury generation

ABSTRACT

Mercury releasing getter devices employing intermetallic compounds of mercury with zirconium and/or titanium such as Zr3Hg and Ti3Hg related compositions of matter and uses thereof to charge electron tubes with mercury.

Unite States Patent 1 Porta et al.

[4 1 Mar. 27, 1973 MERCURY GENERATION Inventors: Paolo Della Porta;Mauro Rebaudo,

both of Milan, Italy Assignee: S.A.E.S. Getters S.p.A., Milan, ItalyFiled: Jan. 18, 1972 Appl. No.2 218,755

Related U.S. Application Data Division of Ser. No. 78,839, Oct. 7, 1970,Pat. No. 3,657,589.

U.S. Cl ..316/3 Int. Cl ..H01j 9/38 Field of Search ..316/3, 4, 16, 24,25;

[56] References Cited UNITED STATES PATENTS 3,318,649 5/1967 Keller eta1. ..3 1 6/3 3,401,296 9/1968 Rigot ..316/16 X Primary Examiner-CharlesW. Lanham Assistant ExaminerJ. W. Davie Att0rneyDavid R. Murphy et al.

[57] ABSTRACT Mercury releasing getter devices employing intermetalliccompounds of mercury with zirconium and/0r titanium such as Zr Hg and Til-lg related compositions of matter and uses thereof to charge electrontubes with mercury.

7 Claims, 7 Drawing Figures MERCURY GENERATION CROSS REFERENCE TORELATED APPLICATIONS the art. In the past these tubes have usually beencharged with mercury in its liquid form. However, such a proceduresuffers from a number of disadvantages inherent in the storage andhandling of liquid mercury due to its toxicity and other difficultiesinherent in the handling of a liquid metal.

There is present in the art a long felt need for an alternative to theuse of liquid mercury. It has been proposed to introduce mercury intoelectron tubes in the form of a thermally decomposable compound ofmercury. Examples of such prior attempts are disclosed in Rigot U.S.Pat. No. 3,401,296 relating to the use of mercury pyrophosphate. Anotherprocedure is by the use of a compound of mercury such as mercuric oxideand a reducing agent for the compound of mercury such aszironium-aluminum alloy as described in della Porta et al. U.S. Pat. No.3,385,644. Unfortunately, the use of compounds of mercury suffers from anumber of disadvantages such as the inherent danger of releasing noxiousgases such as oxygen during mercury release.

The release of mercury after the tube has been evacuated and sealed isconsidered dangerous, if not impossible as the release of oxygen andother gases cause a loss of vacuum and other harmful effects within thetube.

Even if oxygen or other gases are released while the tube is beingevacuated, due to mercury generation during the evacuation, the oxygenor other gases can still have harmful effects within the tube, on theelectrodes for example.

To minimize the danger of release of oxygen it has been proposed to mixthe mercury releasing compound with a non-evaporable getter metal suchas zirconium. The intended function of this getter material is to sorbthe noxious gases which may be released concurrently with mercuryrelease from the compound of mercury.

Another disadvantage of the use of mercuric oxide and a reducing agentis the relatively low temperature of approximately 250 C at which themercury releasing reductive reaction takes place. This relatively lowtemperature places an upper limit upon the temperature to which theelectron tube can be raised during the degassing procedure which underconventional manufacturing techniques frequently precedes mercuryrelease.

In an attempt to overcome the disadvantages inherent in the use ofcompounds of mercury it has been suggested in Keller et al US. Pat. No.3,318,649 to employ an alloy of mercury with magnesium.

Keller also suggests the use of a ternary alloy of mercury, magnesiumand nickel.

However, it has been shown that binary alloys of magnesium and mercuryhave generally proved unsatisfactory because of the low temperature atwhich mercury is released. When the mercury recombines with themagnesium undesirable gases which may have been sorbed by the magnesiumcan be released. Furthermore, evaporation of magnesium can take place atthe low temperature at which the mercury is released.

The addition of nickel to form a ternary alloy as suggested by Kellerhas led to only relatively limited improvements.

Another disadvantage of prior mercury vapor releasing compositions isthe relatively low weight percent, frequently less than 10 weightpercent, of releasable mercury.

Accordingly, it is an object of the present invention to provide animproved mercury releasing getter device, an improved mercury vaporgenerating composition and an improved method of charging an electrontube with mercury all of which are substantially free of one or moredisadvantages of the prior art.

Another object is to provide a means by which mercury can be generatedin evacuated and sealed electron tubes which avoids the danger of gasrelease.

Another object is to provide a means for mercury generation which avoidsthe danger of concurrent oxygen release.

A further object is to provide means for mercury generation which doesnot limit the temperature at which high temperature degassing can beperformed.

A still further object is to provide means for mercury generationemploying a noxious gas sorptive nonevaporable getter material whichafter mercury release has a sufficient sorptive capacity to performgettering functions throughout the life of the tube.

Yet another object is to provide a mercury vapor generating compositionwhich has a high weight percent of releasable mercury.

Additional objects and advantages of the present invention will beapparent by references to the following detailed description thereof anddrawings therein:

FIG. 1 is a top view of a mercury releasing getter device of the presentinvention.

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a top view of a modified mercury releasing getter device ofthe present invention.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

FIGS. 5 and 6 are further mercury releasing getter devices.

FIG. 7 is a perspective view of a fluorescent lamp electrode employing agetter device of the present invention.

According to the present invention, there is provided a mercuryreleasing getter device comprising a holder and a mercury vaporgenerating composition carried by the holder, wherein the mercury vaporgenerating composition is an intermetallic compound of mercury and oneor more metals selected from the group consisting of zirconium andtitanium.

The preferred intermetallic compounds useful in the present inventionare those of the formula:

Zr Ti I-Ig,

wherein x and y have any value from 0 to 13 with the proviso that thesum ofx and y is any value from 3 to 13 and z is l or 2. Examples ofsuitable compounds of the aforementioned formula include among others ZrTiHg, Zr Ti Hg, Zr Ti I-Ig Zr Hg, Ti Hg, as well as Zr flg and Ti flg.As described by Pietrokowsky in Journal of Metals" February 1954) pages2l9226, Ti Hg has two crystalline forms, namely 8Ti I-Ig and yTi Hg.

In the present invention both are suitable because the temperature atwhich they release mercury is high enough to permit degassing at hightemperatures without danger of mercury release and still is low enoughto avoid danger of melting or warping the holder.

The preferred intermetallic compounds employed in the present inventionare characterized by having properties, such as for example, thermalstability, different from those that could be foreseen based upon theproperties of the individual components. Furthermore, theseintermetallic compounds have characteristic xray diffraction spectra.They can be produced by a variety of known procedures such as thosedescribed by Pietrokowsky, supra.

The intermetallic compound can be employed in any physical form such asa block, a strip or the like but is preferably employed as a finelydivided particulate solid and generally that which passes through a U.S.standard screen of 10 mesh per inch and preferably that which passesthrough a screen of 70 mesh per inch. Even very fine particles such asthose which pass through a screen of 600 mesh per inch can also beemployed.

Although the above described intermetallic compounds can be employedalone, in another embodiment of the present invention they are mixedwith a nonevaporable getter material. These non-evaporable gettermaterials are characterized by (1) a sorptive capacity for noxious gasessuch as oxygen, carbon monoxide, and water vapor, and (2) a vaporpressure at 1000 C of less than 10 torr. Examples of suitablenon-evaporable getter materials include among others zirconium,titanium, tantalum, niobium, vanadium and mixtures thereof, alloysthereof with one another and with other metals such as aluminum, whichalloys have satisfactory gettering properties. The preferrednonevaporable getter material is an alloy of from 5 to 30 and preferably13 to 18 weight percent aluminum balance zirconium. The most preferredgetter metal is one of 16 percent aluminum balance zirconium availablefrom SAES Getters S.p.A. Milan, Italy, under the trademark St 101.

The non-evaporable getter material can be employed in any suitablephysical form but is preferably employed as a finely divided particulatesolid such as one passing through a U.S. standard screen of 10 mesh perinch and preferably that passing through a screen of 70 mesh per inchand being retained on a screen of 600 mesh per inch. In one embodimentthe mixtures of particulate mercury releasing intermetallic compound andparticulate getter material is pressed into the cavity of an annularring whereas in another embodiment this mixture is pressed onto a thinmetallic substrate. The weight ratio of intermetallic compound to gettermaterial can vary widely but generally is 100:1 to 1:100 and preferably50:1 to 1:50. At greater ratios of mercury releasing compound the gassorptive capacity of the residue is not substantially increased by thegetter material. At lower ratios of mercury releasing compound thepercentage of releasable mercury in the mixture decreases to animpractical level.

The holder can be in any physical shape which will carry the mercuryvapor generating composition. In one embodiment the holder is an annularring similar to that commonly employed to hold vaporable getter metalssuch as barium. In another embodiment the holder is a substrate which ispreferably metallic and which has the particulate mercury vaporreleasing composition embedded in at least one of its surfaces.

The same substrate may be used as a support for other materials whichmight be useful within the tube such as getter materials.

In a further embodiment the holder is in the form of a wire or rodaround which is formed a pill or pellet of the mercury vapor releasingcomposition.

The present invention is applicable to a wide variety of mercurycontaining electron tubes examples of which include among othersthyratrons, fluorescent light tubes, lasers, mercury rectifiers, varioustype of alpha numerical display tubes.

Referring now to the drawings and in particular to FIGS. 1 and 2 thereis shown a mercury releasing getter device 10 of the present invention.In the getter device 10 the holder is in the form of an annular ring 11having a cavity 12, and a mercury vapor releasing composition 13 withinthe cavity 12.

Referring now to FIGS. 3 and 4 there is shown a getter device 30 whichis connected to a similar getter device 30' which in turn is connectedto yet another similar getter device 30". The getter devices 30, 30,30", etc. form a continuous running length of devices. In the device 30the holder is in the form of a substrate 31 having the mercury releasingcomposition 32 in particulate form partially embedded in the upper andlower planar surfaces of the substrate 31. In operation the getterdevice 30 for example is separated from the devices 30 and 30" bysevering the substrate 31 in the vicinity of the small bridgingattachments 33, 34, 35 and 36.

FIG. 5 shows a mercury evaporating getter device 50 in the form of apellet in which the holder is in the form of a rod 51 having the mercuryreleasing composition 52 compressed around and supported by said rod.

FIG. 6 shows a mercury evaporating getter device in the form ofa pelletin which the holder 61 is a wire of high ohmic resistance in the form ofa heating coil 62 around which is formed the mercury releasingcomposition 63.

According to another aspect of the present invention there is providedan improved method for charging an electron tube with mercury comprisingthe steps of inserting into the tube the above described mercuryreleasing compositions preferably by means of one of the above describedgetter devices and then heating the composition to liberate the mercury.The heating can be accomplished by any suitable means such as byradiation, by high frequency induction heating, or by passing a currentthrough the getter device when it is constructed of a material of highohmic resistance. The

heating is conducted at a temperature which will liberate the mercuryfrom the mercury releasing composition. To a certain extent thistemperature will be dependent upon the composition of the intermetalliccompound. For Ti l-Ig and Zr I-Ig a temperature above 500 C andpreferably from 550 C to 950 C is suitable. At temperatures much below500 C mercury is not released whereas at temperatures above 950 C therelease is so rapid that a danger of creating loose particles by thermalfracturing of the alloy exists. Another disadvantage of employingtemperatures above 950 C is the danger of undesirable noxious gasrelease from adjacent portions of the electron tube which tend to alsobe heated.

An important feature of the present invention is that the thermaldecomposition of the intermetallic compound of zirconium and/or titaniumwith mercury leaves the zirconium and/or titanium gas sorptive such thatit functions as a getter metal throughout the life of the tube. Theheating of the composition to release mercury is sufficient to activatethe getter metal.

Another important feature of the present invention is the ability to addother chemical compositions in mixture with the mercury releasingcompound.

The invention is further illustrated by the following examples in whichall parts and percentages are by weight unless otherwise indicated.These non-limiting examples are illustrative of certain embodimentsdesigned to teach those skilled in the art how to practice the inventionand to represent the best mode contemplated for carrying out theinvention.

Example 1 This example illustrates the synthesis of an intermetalliccompound useful in the present invention.

Particulate titanium (143.7g) which passes through a standard screenwith 400 mesh per inch .is placed in a stainless steel crucible withmercury (200.6g)'. The crucible is then closed and heated to about 800 Cfor about 3 hours. The resultant alloy is determined by X- raydiffraction to consist essentially of the compound 'yTi l-lg.

Example 2 The procedure of Example 1 is repeated employing the sametimes, conditions and ingredients except that the titanium is replacedby zirconium (273.7g). I

The resultant alloy is determined tO'COIlSlSI essentially of thecompound Zr I-lg.

Example 3 This example illustrates the use of an intermetallic compoundand a non-evaporable getter material.

The 'yTi l-lg (200mg) of Example 1 is mixed with St 101 alloy (200mg).Both the Ti I-Ig and the St 101 alloy are of particle size such thatthey pass through a screen of 400 mesh per inch. The resultant mixtureis pressed into an annular ring to produce a mercury releasing getterdevice similar to the device shown in FIGS. 1 and 2, containing acoherent particulate composition 13.

This device is mounted in an electron tube and heated by surrounding thedevice 10 with a high frequency induction coil to heat the getter device10 to 950 C for 30 seconds to release at least 60 mg of the mercury andactivate the St 101 alloy.

Example 4 This example illustrates the manufacture and use of mercuryreleasing getter devices similar to those shown in FIGS. 3 and 4.

A mixture of Ti l-Ig (100g) and St 101 (100g) is placed on a substrateof steel and pressed into the substrate as described in Italian Pat. No.746,551 and US. application Ser. No. 33,794 filed May 1, 1970 to producea strip of getter devices in which the mixture is distributed with adensity of 30 mg/cm similar to that shown in FIGS. 3 and 4 of theannexed drawings.

The getter device 30 is then placed in a vacuum tube which is thenevacuated and the device 30 is heated to 850900 C for 15 to 20 secondsto release mercury and activate the St 101 getter metal. The tubefunctions properly with respect to its mercury environment whilecontinuing to sorb gases within the tube.

Example 5 The procedure of Example 4 is repeated except that the slitsforming the bridging attachments 33, 34, 35 and 36 are omitted and theresultant strip 31 formed into a circle around a fluorescent lampelectrode as shown in FIG. 7.

Examples 68 These examples illustrate the synthesis of additionalintermetallic compounds.

The procedure of Example 1 is repeated except that the quantity oftitanium employed is increased as shown in Column 2 of the followingtable to produce the compound shown in Column 3 of the table. All thecompounds shown in the table have mercury releasing temperatures higherthan that of Ti Hg.

1 2 3 Example Quantity of Titanium Compound 6 191.6 Ti,Hg 7 239.5 Ti Hg8 287.4 Ti Hg Example 9 This example illustrates the synthesis of aternary intermetallic compound of the formula Ti Zr Hg Particulatetitanium-zirconium alloy (208.7g) having 34.1 percent titanium balancezirconium which passes though a standard screen with 400 mesh per inchis placed in a stainless steel crucible 'with mercury (200.6g). Thecrucible is then closed and heated to about 800 C for about 3 hours. Theresultant intermetallic compound when heated releases mercury at atemperature approximately C higher than for either Ti I-Ig or Zr I-Ig.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention as described above and as defined inthe appended claims.

What is claimed is:

l. A method for charging an electron tube with mercury comprising thesteps of:

1. inserting into the tube an intermetallic compound of mercury and oneor more metals selected from the group consisting of zirconium andtitanium, and then,

II. heating the inter-metallic compound to liberate the mercury.

2. A method of claim 1 for chargingan electron tube with mercurycomprising the steps of:

l. inserting into the tube a composition comprising:

A. an intermetallic compound of mercury and one or more metals selectedfrom the group consisting of zirconium and titanium, and B. anon-evaporable getter material and then: 11. heating the alloy toliberate the mercury.

3. The method of claim 2 wherein the weight ratio of A13 is 100:1 to1:100.

4. A method for charging an electron tube with mercury comprising thesteps of:

I. introducing Ti l-lg into the vessel: II. closing the vessel: Ill.heating the Ti Hg to a temperature above 550 C to release the mercury.5. A method of claim 1 for charging an electron tube with mercurycomprising in sequence the steps of:

I. inserting into the tube a composition of matter comprising: A.particulate Ti l-lg and B. a particulate alloy of to 30 weight percentaluminum balance zirconium, wherein the ratio of AB is 50:1 to 1:50.

II. evacuating the tube: III. sealing the tube: IV. heating thecomposition of matter to a temperature of 550 to 950 C to decompose theTi I-Ig releasing mercury, and to activate the zirconiumaluminum alloyand render it gas sorptive. 6. A method for charging an electron tubewith mercury comprising the steps of:

I. inserting into the tube an intermetallic compound of the formula:

wherein x and y have any value from O to 13 with the proviso that thesum ofx and y is any value from 3 to 13 and z is 1 or 2, and then,

II. heating the intermetallic compound to liberate mercury.

7. A method for charging a fluorescent light tube with mercurycomprising the steps of:

I. introducing Ti Hg into the tube,

II. closing the tube,

III. heating the Ti I-Ig to a temperature above 550 C to release themercuryv

2. A method of claim 1 for charging an electron tube with mercurycomprising the steps of: I. inserting into the tube a compositioncomprising: A. an intermetallic compound of mercury and one or moremetals selected from the group consisting of zirconium and titanium, andB. a non-evaporable getter material and then: II. heating the alloy toliberate the mercury.
 3. The method of claim 2 wherein the weight ratioof A:B is 100: 1 to 1:100.
 4. A method for charging an electron tubewith mercury comprising the steps of: I. introducing Ti3Hg into thevessel: II. closing the vessel: III. heating the Ti3Hg to a temperatureabove 550* C to release the mercury.
 5. A method of claim 1 for chargingan electron tube with mercury comprising in sequence the steps of: I.inserting into the tube a composition of matter comprising: A.particulate Ti3Hg and B. a particulate alloy of 5 to 30 weight percentaluminum balance zirconium, wherein the ratio of A:B is 50:1 to 1:50.II. evacuating the tube: III. sealing the tube: IV. heating thecomposition of matter to a temperature of 550* to 950* C to decomposethe Ti3Hg releasing mercury, and to activate the zirconium-aluminumalloy and render it gas sorptive.
 6. A method for charging an electrontube with mercury comprising the steps of: I. inserting into the tube anintermetallic compound of the formula: ZrxTiyHgz wherein x and y haveany value from 0 to 13 with the proviso that the sum of x and y is anyvalue from 3 to 13 and z is 1 or 2, and then, II. heating theintermetallic compound to liberate mercury.
 7. A method for charging afluorescent light tube with mercury comprising the steps of: I.introducing Ti3Hg into the tube, II. closing the tube, III. heating theTi3Hg to a temperature above 550* C to release the mercury.